Flash Butt Welder: Butt Welding or Flash Welding?

Posted on Jan 19, 2021

Flash Butt Welder

There is a wide range of flash butt welding machines out there, and you can typically categorize them into stationary and mobile types. The stationary models incorporate systems mainly used in large welding plants for joining short or long rails. The mobile units, on the other hand, incorporate mobile welding systems that are used to produce continuous track sections directly in a track.

What Is a Flash Butt Welder?

A flash butt welder, or a flash butt welding machine, utilizes a reliable joining technology – commonly known as the flash butt welding process – to produce optimal results with the lowest defective rates. It is common to confuse flash butt welding with butt welding, which is an earlier form of welding technique. Therefore in this article, we'll mainly discuss both processes over the course of their development as well as how they differ from each other.

Adding to the above, there is a wide range of flash butt welding machines out there, and you can typically categorize them into stationary and mobile types. The stationary models incorporate systems mainly used in large welding plants for joining short or long rails. The mobile units, on the other hand, incorporate mobile welding systems that are used to produce continuous track sections directly in a track. Both types of flash butt welding machines are capable of producing high-quality welds for nearly all types of components used for turnouts.
 

How does Butt Welding Work?

As one of the earliest forms of resistance welding, butt welding was widely used in the metalworking industry in the early days. Although it works very similarly to the modern form of butt welding, the notable distinction lies in the applications of pressure and current. 

Despite the prevalence of butt welding in the early industrial years, it wasn't always available because of the high pressure required to bring the attaching ends of large workpieces to the forming temperature. The preparation was much more hideous and required more caution. Operators of welding machines would have to make sure that the surfaces are clean, smooth, and parallel. Had proper preparation not been undertaken, hot spots would have been created on the weld face due to an uneven current flow.

In a basic butt weld, the parts to be welded are first joined under pressure, followed by applying a current that heats the contact area enough to permit the applied pressure to bring the workpieces together. In other words, a butt weld in the early days is a single-stage process involving both pressure and current, both of which are applied throughout the entire cycle until the joint becomes plastic. The constant pressure softens the area, creating the forging effect and the following welded joint. In essence, the key is to have both the pressure and current remain unchanged throughout the weld cycle.
 

:: Read More: All You Need to Know about Flash Welder

How does Flash Butt Welding Work?

The flash butt welding process, being the improved form of butt welding, is a type of electrical resistance welding method used for joining components. The term "flash" is relative to a "flashing" action produced in the welding process, during which heat is transferred by the flash action resistance at the surface instead of contract resistance – as in butt welding. 

Contrary to the above, flash butt welding is a two-stage process. The first stage is the flashing action in which current is applied to the workpieces, producing a flashing across the surface of the two butting ends of the parts. Instead of utilizing pressure and current, the flashing method is used to bring the material to a plastic state. This flashing action creates a HAZ similar to a butt weld. Once the proper temperature is reached and the part becomes plastic, the second stage (i.e., the forging action) begins. The two ends of the parts are joined with a strong force, enough to cause the material to upset. This forces the plastic metal with impurities out of the joint.
 

How do Both Welding Methods Differ?

So what makes flash butt welding a better method than butt welding other than what we already illustrated above? The first advantage is better control: the supplement of electronic and microprocessor controls can accurately monitor the flash welding process. These controls include current monitoring, flash voltage action, and feedback information to determine the acceleration and velocity of the two parts being welded. 

Another significant advancement is the additional stages, which manifest themselves by the mechanism of pre-flash and preheating. Pre-flash, or a burn-off, enables the ragged ends of a part to be squared up before moving to the second stage, the preheating. The preheating portion of the flash welding process allows heat to be generated into the surface of the weld while keeping material lost to the minimum. 

To elaborate further, the preheating action is the oscillation of two components against each other. When the two ends of workpieces join, the resistance allows heat to be produced, and the two ends are separated before becoming molten, enabling a cooling effect at the interface of the material. When the ends begin to cool off, the process repeats rapidly until heat is generated back into both parts. And once the HAZ has been achieved, the flash weld stage continues briefly, followed by the forging force or the upset.
 

Conclusion

In summary, flash butt welding is by no means limited to only railroad applications. The technology develops so rapidly that the application for flash butt welding (and even butt welding) is changing constantly as well. Things like advanced controls, AC and DC power sources, development of hydraulics, and servo valves have all contributed to the improved process, broadening the applications that can be performed.

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